Relaying is being considered e.g. for Long Term Evolution (LTE) Release 10, as a tool to improve the coverage of high data rates, group mobility, temporary network deployment, the cell-edge throughput and/or to provide coverage in new areas. At least type-1 relay nodes are part of LTE-Advanced, and a type-1 relay is an inband relaying node (RN), characterized by a serial of characteristics, e.g. having its own physical cell ID, appearing as a Rel-8 eNB to Rel-8 user equipments (UEs) etc.
It is generally assumed in 3rd Generation Partnership Project (3GPP), which the LTE endeavourments form part of, that the transmission from any antenna of a relaying node may cause severe interference to the reception of the other antenna, see FIG. 1A and FIG. 1B, respectively. In order not to set strict requirements to user equipments and network deployment, 3GPP assumes that Un, i.e. the radio link between the base station (eNB) and the relaying node (RN), and Uu, i.e. the radio link between the relaying node (RN) and the user equipment (UE), of the same relaying node, are operated in different time.
Thus in the radio link from the base station (eNB) to the relaying node (RN), and the radio link from the relaying node (RN) to the user equipment (UE) are time division multiplexed in a single frequency band. Thereby only one of these links is active at any time, in order not to cause interference on the other.
The same applies also in the uplink, such that the radio link from the relaying node (RN) to the base station (eNB), and the radio link from the user equipment (UE) to the relaying node (RN) are time division multiplexed in a single frequency band. Thereby only one of these links is active at any time.
In this way, the relaying node defined in 3GPP can only work in half-duplex mode. When operating in half-duplex mode, communication is possible in both directions i.e. from the user equipment via the relaying node to the base station, but only in one direction at a time, not simultaneously. Typically, once a node begins receiving a signal, it must wait for the transmitter of the transmitting node to stop transmitting, before replying.
Though network deployment efforts and hardware requirements may not be a problem for type-I relay, such a half-duplex mechanism leads to undesirable performance loss, as resources have to be partitioned between Un and Uu.
Thus the over all transmission performance is suffering, in comparison with transmission in full duplex mode, which allows communication in both directions simultaneously.
Another problem with the known solution for avoiding self interference at the relaying node is that the time partitioning creates a delay of the transmission, which prolongs the over all transmission time.